diff --git a/src/calibre/gui2/viewer/main.py b/src/calibre/gui2/viewer/main.py
index c6eb76c735..207af7d510 100644
--- a/src/calibre/gui2/viewer/main.py
+++ b/src/calibre/gui2/viewer/main.py
@@ -507,8 +507,9 @@ class EbookViewer(MainWindow, Ui_EbookViewer):
         self.clock_label.setVisible(True)
         self.clock_label.setText('99:99 AA')
         self.clock_timer.start(1000)
-        self.clock_label.setStyleSheet(self.clock_label_style%
-                tuple(self.view.document.colors()))
+        self.clock_label.setStyleSheet(self.clock_label_style%(
+                'rgba(0, 0, 0, 0)',
+                self.view.document.colors()[1]))
         self.clock_label.resize(self.clock_label.sizeHint())
         sw = QApplication.desktop().screenGeometry(self.view)
         self.clock_label.move(sw.width() - self.vertical_scrollbar.width() - 15